I wrote to al-Ṣādiq عليه السلام asking him about the meaning of ‘Allāh’, He replied: He has authority over what is minute and what is grand.1

1. Here the Imām عليه السلام explains the meaning of Allāh by stating that His authority embraces everything, even:
a) that which is minute (i.e. small) – even that which cannot be seen by the naked eye, like atoms, which can only be seen by a microscope.
b) that which is grand (i.e. big) – such as the planets and galaxies.
In other words there’s nothing that is outside His authority and power as the Qur’ān states many times: ‘Indeed Allah is over all things powerful’.